The invention relates to an electro-hydraulic control device for an automatic automobile transmission.
It is possible to preselect various operating stages such as forward travel, rearward travel, neutral, or parking position from an operating device in the automobile. In automatic transmissions, depending on the operating modes selected, clutches and brakes are operated through a hydraulic control. Generally, the effective connection from the operating element inside the vehicle to the electro-hydraulic control device in the automatic transmission is implemented mechanically, e.g., by Bowden cables. However, it is also possible to implement the effective connection between the operating element and the transmission control purely electrically. This has the advantage of being able to select the location of the operating element freely inside the vehicle. As in case of an electric effective connection, the parking mechanism cannot be released or engaged mechanically using the Bowden cable, the parking mechanism must be engaged via a spring storage device and released hydraulically. DE 43 22 523 A1 describes an electro-hydraulic control device of an automatic automobile transmission in which the effective connection between the operating device inside the motor vehicle and the electro-hydraulic control device can be electrical and the electro-hydraulic control device is designed such that the operating stages D, R, and N are selected by pressurizing individual shifting elements while stage P is selected by depressurizing all switching elements.
This means that not only in operating stage P, but also in all the operating stages of the selector lever the parking mechanism is engaged when the pressure fails. In order to be able to unlock the engaged parking mechanism if the electrical voltage supply fails or if there is a defect in the electronic control device, an emergency unlocking device is disclosed by means of which the parking mechanism can be unlocked mechanically.
In an automatic transmission it is necessary to be able to move the vehicle when the electronic control device fails, at least at one engaged gear, with the parking mechanism released, by the driving force of the engine. With a mechanically effective connection between the operating element in the passenger compartment and the automatic transmission, this emergency travel program, as well as the unlocking of the parking mechanism, are effected by mechanical switching of a hydraulic valve in the electro-hydraulic control of the automatic transmission. With an electrically effective connection between the operating element in the passenger compartment and the automatic transmission, there is no possibility of engaging the emergency travel program and unlocking the parking mechanism from the operating element.
The goal of the invention is to provide a control for an automatic automobile transmission in which the operating stages D, R, and N as well as P can be preselected by an operating device inside the passenger compartment and an electrical connection between the operating device and the automatic transmission, with the parking mechanism being engaged by a spring storage device and released hydraulically, and in which the parking mechanism can be released manually if the electronic transmission control fails so that the transmission is automatically switched to an emergency travel program in order to be able to operate the vehicle in a previously selected gear.
In addition, it must be possible to operate the vehicle further during forward travel until the combustion engine stops and to automatically engage the parking mechanism during rearward travel if the electronic transmission control fails.
According to the invention, this goal is achieved by a type-compliant transmission control that also includes the features of the main claim.
According to the invention, the electronic-hydraulic control device of an automatic automobile transmission is designed such that operating stages D, R, and N are selected by pressurizing individual switching elements while operating stage P is selected by depressurizing all shifting elements. As a result, the parking mechanism is engaged in operating stage P and in all the other operating stages of the selector lever if the pressure fails. The hydraulic control unit is designed such that the various gears are selected by the electronic control device energizing solenoid valves thereby switching control valves that in turn control the actuators for friction clutches or brakes. If the electronic control device fails, the solenoids are de-energized, and, in reverse gear, the control valves are controlled so that the actuators of the friction clutches or brakes as well as the parking mechanism have zero pressure. This has the advantage that if the electronic control device fails, the force connection between the drive motor and the output shaft of the transmission is interrupted and the parking mechanism is activated at the same time. By manually displacing the parking mechanism by a lever outside the transmission, the parking mechanism can be released in an emergency while simultaneously a valve is switched so that the pressure produced by a pump activates control valves to pressurize actuators so that a forward gear is engaged. Therefore, when the vehicle has stopped parking mechanism, a forward travel direction can be selected automatically by emergency-unlocking the parking mechanism so that the vehicle can start again.
When the parking mechanism has been emergency-unlocked, it remains unlocked and the preselected gear remains selected parking mechanism until the parking, mechanism is locked again manually. If the vehicle is moving rearwards when the electronic control device fails, the actuators for the friction clutches or brakes are depressurized by de-energizing all solenoid valves, and the adhesion between the drive motor and the output shaft of the transmission is interrupted. At the same time, the-valve controlling the clutch for the reverse gear is activated in such a way that when the parking mechanism is emergency-unlocked, the forward gear can be selected again.
The valves are preferably controlled such that when the valves are de-energized due to a failure of the electronic control device during forward travel, an emergency gear is selected automatically and the parking mechanism remains disengaged until the combustion engine is switched off, and, if the electronic control system fails during rearward travel, all clutches and brakes are opened so that the reverse gear is disengaged and the parking mechanism is engaged automatically.